Design a Dropbox-like file sync service
Overview
This question evaluates a candidate's ability to design large-scale distributed file storage and synchronization systems, testing competencies in data modeling, consistency and conflict resolution, chunking/delta sync, durability, security, and operational concerns like observability and disaster recovery.
Meta
Jul 15, 2025, 12:00 AM
Software Engineer
Onsite
System Design
0
0
Design a Dropbox-like File Storage and Sync Service
You are asked to design a cross-device file storage and synchronization service at internet scale (hundreds of millions of users). The system must support multi-device sync, offline edits, and reliable sharing—with strong durability and clear consistency guarantees.
Functional Requirements
- Multi-device sync across desktop and mobile
- Offline edits with eventual synchronization
- Conflict detection and resolution
- Large file support with chunking and delta sync
- Deduplication and compression
- Versioning and restore
- Sharing with ACLs (users, groups, link sharing)
- Near real-time notifications
- Quota and billing support
Non-Functional Requirements
- Scale to hundreds of millions of users and billions of files
- High durability and availability across regions
- Clear consistency model for metadata and content
- Mobile constraints (battery, background limits, metered networks)
- Encryption options: client-side (E2EE) and server-side
- Observability: metrics, logs, tracing, integrity checks
- Disaster recovery with defined RPO/RTO
Deliverables
Provide:
- High-level architecture: clients and sync engine, metadata service, blob storage/CDN
- Data model: files, chunks, versions, tombstones, ACLs, journals
- Read and write flows (including conflict and delta sync)
- Consistency model and guarantees
- Strategies for hotspots, backfills, and migrations
- Notes on mobile constraints, encryption options, quota/billing, observability, and disaster recovery
Solution
Login required
Show